Recently, to reproduce the instrumental sounds of high quality in an electronic piano, actual instrumental sounds were sampled and stored in a memory as pulse code modulation waveform data, and the data was read from the memory for the reproduction of the instrumental sounds. When the pulse code modulation waveform data was stored in the memory for all the keys and all the key press intensities of the electronic piano, however, the voluminous memory was required.
To reduce the memory capacity, in a conventional electronic instrument sound source system, as shown in FIG. 7, only the pulse code modulation waveform of strong key presses is sampled. To obtain the waveform of weak key presses, the sampled waveform of the strong key press is transformed via a low pass filter into the waveform only of low order harmonic components. The pulse code modulation waveform of strong key presses and the filtered waveform composed of weak key press components are mixed in a specified rate, thereby forming the waveform of moderate key presses.
Actual strong and weak presses on piano keys differ from each other in the kind of harmonic components, and also in the relative content rate of reference and harmonic sound components. In the conventional sound source system, the relation between the reference and harmonic sound components in the weak key press data is only the same as that in the strong key press data. The relation subtlely varying with key press intensities as in the actual piano sounds is unobtainable. Just the monotonous relation can be provided.
To obtain the relation variable with the key press intensities between the reference and harmonic sound components, the pulse code modulation waveform at least of weak and strong key presses are sampled. By synthesizing the sampled waveforms in a specified rate, in the conventional sound source system, as shown in FIG. 8, the waveform of instrumental sounds of moderately pressed keys is formed. This sound source system, however, has following disadvantages.
As aforementioned, strong key press differs from weak key press in the kind of harmonic components, as well as in the relative content ration of the reference and harmonic sound components. Furthermore, the strong key press slightly differs from the weak key press in the phase of waveform. When the waveforms different from each other in the phase are synthesized, the phase interference arises, thereby forming the waveform different from the waveform, shown by dotted lines in FIG. 8 of the sounds to be reproduced of the actually moderately pressed keys. In the formed waveform, the level of harmonic components is changed because of the phase interference.
As aforementioned, when the strong and weak key press waveform data is based on the same sampled waveform, only monotonous and shallow sounds are reproduced. When the strong and weak key press waveforms are individually sampled, however, the instrumental sounds excessively different in balance from the actual instrumental sounds are reproduced.